This invention relates to a method for producing a composite material with oriented, reinforcing, discontinuous fibers.
The use of composite materials has been rapidly expanding in modern production technologies. With the costs of composite materials and production technologies dropping further these materials are expected to break out of the aerospace into automotive and industrial markets. There are three basic state of the art technologies for production of high strength composites:
1. The product is sequentially laminated using prefabricated woven fabric from high strength fibers and a suitable resin to impregnate and bind together the layers. This technique is used mostly to produce shell-shaped products (boat hulls, car bodies, airplane wings and fuselage, etc.). Different high strength fibers (glass, carbon, aramids) are available in many different patterns of woven fabric. Sequential layering is labor intensive. It is difficult to optimally use the reinforcing material since the fiber orientation within the product is constrained by the use of prefabricated patterns and the layering technique.
2. Direct incorporation of high strength fibers into the product. This technique works best for profiles where relatively simple machines can lay down the fibers in the required patterns. It is also commonly used for products of simple shape and function, such as pressure vessels. For complex parts this technique is very expensive.
3. Forming the products from discontinuous fiber (chopped) reinforced resins. This technique is most versatile, but chopped fiber cannot be optimally oriented and this sets a rather low limit on the strength of the composite. Orientation of the chopped fiber is possible with elongational flows, but this is generally limited to extrusion products.